Electrosurgical apparatus with high speed energy recovery

ABSTRACT

A circuit for controlling the discharging of stored energy in an electrosurgical generator includes a pulse modulator which controls an output of a power supply. At least one comparator is configured to provide an error signal to the pulse modulator based on a comparison between an output signal generated by the power supply and a feedback signal generated in response to the application of energy to tissue. A discharge circuit is configured to control the discharge of the output of the power supply to an inductive load disposed in parallel with the output of the power supply based on the comparison between the output signal and the feedback signal. The discharge circuit provides a rapid response and time rate control of the delivered electrosurgical energy by controlling the power supply and delivered RF energy in real time, based on a feedback signal generated in response to the application of energy to tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/205,298, now U.S. Pat. No. 8,287,529, filed on Sep. 5, 2008, entitled“ELECTROSURGICAL APPARATUS WITH HIGH SPEED ENERGY RECOVERY,” thecontents of which are incorporated by reference herein in theirentirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrosurgical system and methodand, more particularly, to an electrosurgical generator configured todynamically control energy output.

2. Background of Related Art

Electrosurgery involves application of high radio frequency electricalcurrent to a surgical site to cut, seal, ablate, or coagulate tissue. Inmonopolar electrosurgery, a source or active electrode delivers radiofrequency energy from the electrosurgical generator to the tissue and areturn electrode carries the current back to the generator. In monopolarelectrosurgery, the source electrode is typically part of a surgicalinstrument held by the surgeon and applied to the tissue to be treated.A patient return electrode is placed remotely from the active electrodeto carry the current back to the generator.

In bipolar electrosurgery, a hand-held instrument typically carries twoelectrodes, e.g., electrosurgical forceps. One of the electrodes of thehand-held instrument functions as the active electrode and the other asthe return electrode. The return electrode is placed in close proximityto the active (i.e., current supplying) electrode such that anelectrical circuit is formed between the two electrodes. In this manner,the applied electrical current is limited to the body tissue positionedbetween the two electrodes.

Conventional electrosurgical generators include a high voltage directcurrent power supply connected to a radio frequency (RF) output stagethat converts DC energy generated by the power supply into RF energy.The power supply includes an output filter which substantiallyeliminates undesirable frequencies (e.g., noise) from the DC energy andstores large amounts of energy. Rapid tissue desiccation during theapplication of RF energy creates a potential for patient burn hazardsdue to excess energy dosage at the tissue site when the power sourcefails to rapidly alter the supplied energy dosage in response withdynamic changes in tissue impedance. Rising tissue impedance levelscaused by desiccation unload the energy source and sustain the energydelivered to the tissue due to the large amount of stored energy in theoutput filter.

SUMMARY

According to one embodiment of the present disclosure, a circuit forcontrolling the discharging of stored energy in an electrosurgicalgenerator includes a pulse modulator which controls an output of a powersupply. At least one comparator is configured to provide an error signalto the pulse modulator based on a comparison between an output generatedby the power supply and a feedback signal generated in response to theapplication of energy to tissue. A discharge circuit is configured tocontrol the discharge of the output of the power supply to an inductiveload disposed in parallel with the output of the power supply based onthe comparison between the power supply output and the feedback signal.

According to another embodiment of the present disclosure, a circuit forcontrolling the discharging of stored energy in an electrosurgicalgenerator includes a pulse modulator which controls an output of a powersupply. At least one comparator is configured to provide an error signalto the pulse modulator based on a comparison between an output generatedby the power supply and a feedback signal generated in response to theapplication of energy to tissue. A discharge circuit has a firstswitching component configured to discharge the output of the powersupply to an inductive load disposed in parallel with the output of thepower supply if the feedback signal is less than the power supply outputand a second switching component configured to control switching of thefirst switching component based on the discharge rate of the output tothe inductive load.

The present disclosure also provides a method for controlling thedischarging of stored energy in an electrosurgical generator. The methodincludes applying energy stored in an output of a power supply totissue. The method also includes generating at least one control signalbased on at least one of a sensed tissue property and a sensed energydelivery property, (i.e. power, voltage, current, time etc.). The methodalso includes generating an error signal based on a comparison betweenthe at least one control signal and the energy stored in the output. Themethod also includes discharging the stored energy to an inductive loadin parallel with the output of the power supply based upon thecomparison between the energy stored in the output and the controlsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1A is a schematic block diagram of a monopolar electrosurgicalsystem in accordance with an embodiment of the present disclosure;

FIG. 1B is a schematic block diagram of a bipolar electrosurgical systemin accordance with an embodiment of the present disclosure;

FIG. 2 is a schematic block diagram of a generator in accordance with anembodiment of the present disclosure;

FIG. 3 is a circuit diagram of a power supply in accordance with anembodiment of the present disclosure; and

FIG. 4 is a flow chart diagram of a method for controlling the dischargeof energy stored in an output of an electrosurgical generator accordingto an embodiment of the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail to avoid obscuring the present disclosure inunnecessary detail.

In general, the present disclosure provides for an electrosurgicalgenerator including a power supply configured to rapidly re-directstored output energy through inductive energy transfer utilizing acontrolled switching circuit to regulate, in real-time, the level ofpower sourced to the RF energy delivered to tissue during treatment.

More specifically, when the generator senses increased impedance intissue due to rapid tissue desiccation, the generator of the presentdisclosure can control, in real time, the amount of treatment energyapplied to tissue through use of a so-called “discharge” circuit. Thedischarge circuit provides a rapid response and time rate control of theelectrosurgical energy delivered to tissue by discharging energy storedin an output filter of the power supply into an inductive load based ona feedback signal generated by the controller. The feedback signal maybe based on a sensed tissue property (e.g., impedance) and/or an energyproperty (e.g., voltage, output energy level, etc.). This controlprovides for more accurate application of target treatment energy levelsto treat tissue.

The generator according to the present disclosure can perform monopolarand bipolar electrosurgical procedures, including vessel sealingprocedures. The generator may include a plurality of outputs forinterfacing with various electrosurgical instruments (e.g., a monopolaractive electrode, return electrode, bipolar electrosurgical forceps,footswitch, etc.). Further, the generator includes electronic circuitryconfigured for generating radio frequency power specifically suited forvarious electrosurgical modes (e.g., cutting, blending, division, etc.)and procedures (e.g., monopolar, bipolar, vessel sealing, ablation).

FIG. 1A is a schematic illustration of a monopolar electrosurgicalsystem according to one embodiment of the present disclosure. The systemincludes a monopolar electrosurgical instrument 2 including one or moreactive electrodes 3, which can be electrosurgical cutting probes,ablation electrode(s), etc. Electrosurgical RF energy is supplied to theinstrument 2 by a generator 20 via a supply line 4, which is connectedto an active terminal 30 (FIG. 2) of the generator 20, allowing theinstrument 2 to coagulate, ablate and/or otherwise treat tissue. Theenergy is returned to the generator 20 through a return electrode 6 viaa return line 8 at a return terminal 32 (FIG. 2) of the generator 20.The active terminal 30 and the return terminal 32 are connectorsconfigured to interface with plugs (not explicitly shown) of theinstrument 2 and the return electrode 6, which are disposed at the endsof the supply line 4 and the return line 8, respectively.

The present disclosure may be adapted for use with either monopolar orbipolar electrosurgical systems. FIG. 1B shows a bipolar electrosurgicalsystem according to the present disclosure that includes anelectrosurgical forceps 10 having opposing jaw members 50 and 55. Theforceps 10 includes a shaft member 64 having an end effector assembly 40disposed at the distal end thereof. The end effector assembly 40includes two jaw members 50 and 55 movable from a first position whereinthe jaw members 50 and 55 are spaced relative to another to a closedposition wherein the jaw members 50 and 55 cooperate to grasp tissuetherebetween. Each of the jaw members 50 and 55 includes an electricallyconductive sealing plate 112 and 122, respectively, connected to thegenerator 20 that communicates electrosurgical energy through the tissueheld therebetween.

Electrically conductive sealing plates 112 and 122, which act as activeand return electrodes, are connected to the generator 20 through cable23, which includes the supply and return lines coupled to the active andreturn terminals 30, 32 (FIG. 2). The electrosurgical forceps 10 iscoupled to the generator 20 at the active and return terminals 30 and 32(e.g., pins) via a plug 92 disposed at the end of the cable 23, whereinthe plug includes contacts from the supply and return lines.Electrosurgical RF energy is supplied to the forceps 10 by generator 20via a supply line connected to the active electrode and returned througha return line connected to the return electrode.

Forceps 10 generally includes a housing 60 and a handle assembly 74 thatincludes moveable handle 62 and handle 72 which is integral with thehousing 60. Handle 62 is moveable relative to handle 72 to actuate theend effector assembly 40 to grasp and treat tissue. The forceps 10 alsoincludes shaft 64 that has a distal end 68 that mechanically engages theend effector assembly 40 and a proximal end 69 that mechanically engagesthe housing 60 proximate a rotating assembly 80 disposed at a distal endof the housing 60.

With reference to FIG. 1B, the generator 20 includes suitable inputcontrols (e.g., buttons, activators, switches, touch screen, etc.) forcontrolling the generator 20. In addition, the generator 20 includes oneor more display screens for providing the surgeon with variety of outputinformation (e.g., intensity settings, treatment complete indicators,etc.). The controls allow the surgeon to adjust power of the RF energy,waveform, and other parameters to achieve the desired waveform suitablefor a particular task (e.g., coagulating, tissue sealing, division withhemostasis, etc.). Further, the forceps 10 may include a plurality ofinput controls which may be redundant with certain input controls of thegenerator 20. Placing the input controls at the forceps 10 allows foreasier and faster modification of RF energy parameters during thesurgical procedure without requiring interaction with the generator 20.

FIG. 2 shows a schematic block diagram of the generator 20 having acontroller 24, a power supply 27, an RF output stage 28, and a sensormodule 22. The power supply 27 may provide DC power to the RF outputstage 28 which then converts the DC power into RF energy and deliversthe RF energy to the forceps 10. The controller 24 includes amicroprocessor 25 having a memory 26 which may be volatile type memory(e.g., RAM) and/or non-volatile type memory (e.g., flash media, diskmedia, etc.). The microprocessor 25 includes an output port connected tothe power supply 27 and/or RF output stage 28 which allows themicroprocessor 25 to control the output of the generator 20 according toeither open and/or closed control loop schemes.

A closed loop control scheme generally includes a feedback control loopwherein the sensor module 22 provides feedback to the controller 24(i.e., information obtained from one or more sensing mechanisms thatsense various tissue parameters such as tissue impedance, tissuetemperature, output current and/or voltage, etc.). The controller 24then signals the power supply 27, which then adjusts the DC powersupplied to the RF output stage, accordingly. The controller 24 alsoreceives input signals from the input controls of the generator 20and/or forceps 10. The controller 24 utilizes the input signals toadjust the power output of the generator 20 and/or instructs thegenerator 20 to perform other control functions.

The microprocessor 25 is capable of executing software instructions forprocessing data received by the sensor module 22, and for outputtingcontrol signals to the generator 20, accordingly. The softwareinstructions, which are executable by the controller 24, are stored inthe memory 26 of the controller 24.

The controller 24 may include analog and/or logic circuitry forprocessing the sensed values and determining the control signals thatare sent to the generator 20, rather than, or in combination with, themicroprocessor 25.

The sensor module 22 may include a plurality of sensors (not explicitlyshown) strategically located for sensing various properties orconditions, e.g., tissue impedance, voltage at the tissue site, currentat the tissue site, etc. The sensors are provided with leads (orwireless) for transmitting information to the controller 24. The sensormodule 22 may include control circuitry which receives information frommultiple sensors, and provides the information and the source of theinformation (e.g., the particular sensor providing the information) tothe controller 24.

More particularly, the sensor module 22 may include a real-time voltagesensing system (not explicitly shown) and a real-time current sensingsystem (not explicitly shown) for sensing real-time values related toapplied voltage and current at the surgical site. Additionally, an RMSvoltage sensing system (not explicitly shown) and an RMS current sensingsystem (not explicitly shown) may be included for sensing and derivingRMS values for applied voltage and current at the surgical site.

The measured or sensed values are further processed, either by circuitryand/or a processor (not explicitly shown) in the sensor module 22 and/orby the controller 24, to determine changes in sensed values and tissueimpedance. Tissue impedance and changes thereto may be determined bymeasuring the voltage and/or current across the tissue and thencalculating changes thereof over time. The measured and calculatedvalues may be then compared with known or desired voltage and currentvalues associated with various tissue types, procedures, instruments,etc. This may be used to drive electrosurgical output to achieve desiredimpedance and/or change in impedance values. As the surgical procedureproceeds, tissue impedance fluctuates in response to adjustments ingenerator output as well as removal and restoration of liquids (e.g.,steam bubbles) from the tissue at the surgical site. The controller 24monitors the tissue impedance and changes in tissue impedance andregulates the output of the generator 20 in response thereto to achievethe desired and optimal electrosurgical effect.

Referring to FIG. 3, there is shown a block diagram of the power supply27 including a control circuit 100 in series with a switching circuit145. The control circuit 100 includes a first comparator 110 (e.g., anoperational amplifier) having positive and negative input pins +A1 and−A1, respectively. Positive input pin +A1 is configured to receive anapplied control signal (e.g., a variable DC voltage) from the controller24 based on any one or more tissue parameters provided by the sensormodule 22. Negative input pin −A1 is configured to receive aproportionally scaled feedback voltage of the power source output (e.g.,connected to the RF output stage 28) to match the applied control signalon input pin +A1, as will be discussed in further detail below.

When the power source output fails to match the applied control signal,the resulting voltage difference at positive and negative input pins +A1and −A1 causes the first comparator 110 to output an analog error signal(e.g., analog voltage) to drive a pulse modulator (“PM”) 115. PM may be,for example, a pulse width modulator, a phase shift modulator or anysuch device known in the art for converting the analog error signal to adigital pulse control signal. The PM 115 converts the analog errorsignal to a digital pulse control signal (e.g., digital voltage) toimplement control of a full-bridge power stage 120 by phase shifting theswitching of one half-bridge with respect to the other. It allowsconstant frequency pulse-width modulation to provide high efficiency athigh frequencies and can be used either as a voltage mode or currentmode controller. More specifically, an AC/DC converter 125 converts anavailable ac signal (e.g., from an ac line voltage) to a de signal todrive the full-bridge power stage 120, the output of which is, in turn,controlled by the digital pulse control signal to reflect the appliedcontrol signal from the controller 24. The resulting controlled outputof the full-bridge power stage 120 drives an output filter 130 (e.g., alow-pass filter), having an inductor 132 and an output capacitor 134, togenerate a DC output voltage V, across the output capacitor 134. Theresulting output voltage V, is converted to RF energy by the RF outputstage 28 and output to the electrosurgical instrument. A feedbackcompensator 140 continuously monitors the output voltage V, (e.g., inputto the RF output stage 28) and, in turn, provides a proportionallyscaled feedback of the power source output to input pin −A1 of the firstcomparator 110 to match the applied control signal from the controller24.

With continued reference to FIG. 3, discharging of energy is achieved inreal-time using an active discharge circuit (ADC) 145—a component of thepower supply 27—that switches inductor 150 using a first switchingcomponent 160 in parallel with the output capacitor 134 to discharge theenergy therefrom, as will be discussed in further detail below. The ADC145 includes a second comparator 180 (e.g., an operational amplifier)having negative and positive input pins −A2 and +A2 operably coupled tothe positive and negative input pins +A1 and −A2 of the first comparator110, respectively. In this manner, the input pins −A2 and +A2 of thesecond comparator 180 continuously monitor the difference between theapplied control signal from the controller 24 on positive input pin +A1and the proportionally scaled feedback of the power source output onnegative input pin −A1.

An inductive load 150 (e.g., an inductor) is connected in parallel withthe output filter 130 and in series with the first switching component160. The first switching component 160 is normally off and may be atransistor, such as a field-effect transistor (FET), metal-oxidesemiconductor field-effect transistor (MOSFET), insulated gate bipolartransistor (IGBT), relay, or the like. A first resistive element 162 isin series with the first switching component 160 and with ground 168,which is known as a source follower circuit. The source follower limitsthe amount of current that flows through the first resistive element162, the switching component 160, and the inductor 150.

In the case of the power source output being greater than the appliedcontrol signal (i.e., −A1>+A1), the switching circuit 145 utilizesinductive energy transfer to rapidly re-direct the stored output energyof the power source 27 away from the RF output stage 28 until the powersource output matches the applied control signal (i.e., −A1=+A1). Morespecifically, the second comparator 180 provides a drive voltagesufficient to close the first switching component 160 to discharge thestored energy from the output capacitor 134 to the inductive load 150.The activation of the first switching component 160 causes a conductioncurrent I_(Q1) to discharge from the capacitor 134 to ground 168 throughthe inductive load 150 and the first resistive element 162 to generatecorresponding voltages V_(Lr) and V_(R1), respectively. That is, whilethe first switching component 160 is switched on, the inductive load 150absorbs the energy discharged by the output capacitor 134 to rapidlydecrease the output voltage V_(c) until the power source output againmatches the applied control signal (i.e., −A1 =+A1). Under this matchcondition, the second comparator 180 no longer provides the sufficientdrive voltage, resulting in the first switching component 160 to returnto the normally off position to interrupt the flow of the conductioncurrent I_(Q1) through the inductive load 150. The interruption ofcurrent flow through the inductive load 150 causes the magnetic fluxfield on the inductive load 150 to collapse due to a backelectromagnetic force of voltage thereacross (e.g., a so-called “backEMF effect”). The back EMF voltage turns on diode 155, connected inshunt with the inductive load 150, to become forward-biased, providing apath for the inductor 150 magnetic flux and conductive current to bereset to zero. In addition this process prevents the back EMF voltagefrom increasing to a level sufficient to cause damage and/or stress toother components of the ADC 145 (e.g., the first switching component160, the first resistive element 162, etc.).

The ADC 145 includes a second normally off switching component 170 thatprovides so-called “turn-on limiting” of the first switching component160 to control the flow of the conduction current I_(Q1) through theinductive load 150. More specifically, the second switching component170 operates to monitor the voltage drop V_(R1) across the firstresistive element 162 caused by the conduction current I_(Q1). Resistors164 and 166 establish the threshold for component 170 turn on limiting.As the conduction current I_(Q1) through the first switching component160 increases, the voltage drop V_(R1) across the first resistiveelement 162 increases to drive the second switching component 170 on,when the threshold for turn on limiting of component 170 is reached. Theturn on of the second switching component 170 effectively reduces thedrive voltage applied to the first switching component 160 to a steadystate value from the second comparator 180, thereby regulating thecurrent flow through the first switching component 160. The resultingreduced drive voltage of the first switching component 160 stabilizesthe flow of conduction current I_(Q1) through the first switchingcomponent 160 and, thus, through the first resistive element 162 therebyregulating the voltage drop V_(R1) thereacross. In this manner, theoutput voltage V_(c) across the output capacitor 134 discharges at anincremental time rate of change, represented by equation (1) below:Vc=1/C*∫ ₀ ^(t) I _(Q1) dt  (1)

Where:

Vc is the output voltage across the capacitor 134;

C is the capacitance of the capacitor 134; and

I_(Q1) is the conductive current through the inductive load 150.

In the illustrated embodiment, one or more resistive elements 164 and166 are utilized to set the desired proportion of the voltage dropV_(R1) across the first resistive element 162 sufficient to turn on thesecond switching element 170. That is, each of resistive elements 164and 166 may be interchanged with resistive elements of variousresistance values to vary the proportion of the voltage drop V_(R1)across the first resistive element 162 at which the second switchingcomponent 170 turns on. For example, the resistance ratio provided bythe combination of the resistive elements 164 and 166, adjusts theproportion of the voltage drop V_(R1) necessary to turn on the secondswitching component 170. The resistive elements 164 and 166 of FIG. 3are illustrative only in that a single resistive element (not explicitlyshown) or, alternatively, a plurality of resistive elements (notexplicitly shown) in parallel and/or in series may replace the resistiveelements 164 and 166 between the first switching component 160 and thesecond switching component 170 to achieve substantially the samepurpose.

A buffer 172 (e.g., one or more resistors) between the first switchingcomponent 160 and the output of the second comparator 180 provides anisolation buffer therebetween when the second switching component 170 isturned on. As seen in FIG. 3, absent the buffer 172, the output of thesecond comparator 180 is shorted to ground 168 due to the closure of thesecond switching component 170. In this way, the buffer 172 operates toprevent a so called “over current” condition on the second comparator180 during the closure of the second switching component 170.

FIG. 4 illustrates a method 200 for controlling the discharge of energystored in an output of an electrosurgical generator. In step 210, energyis supplied to tissue. More specifically, the power supply 27 providesDC power to the RF output stage 28. The RF output stage 28 converts theDC power into RF energy and delivers the RF energy to tissue (e.g., viaforceps 10). In step 220, the sensor module 22 generates a feedbacksignal to the controller 24 based on any one or more sensed tissueand/or energy properties. In step 230, a comparison is made between acontrol voltage generated by the controller 24 in response to the sensorfeedback signal and the output voltage V_(c) sampled by feedbackcompensator 140. In step 240, based on the comparison of step 230, anerror signal is generated by the first comparator 110 and provided tothe PM 115. PM 115 drives the full bridge power stage 120 to develop theoutput voltage Vc on capacitor 134, based on any one or more sensedtissue and/or energy properties. In step 250, the switching circuit 145controls the discharging of the output capacitor 134 by redirecting thepower supply 27 stored energy using the inductive load 150 in responseto a reduction of required RF energy delivered to the tissue, based onany one or more sensed tissue and/or energy properties. Sensor module 22provides feedback to controller 24 regarding the reduced RF energy need,whereby controller 24 then communicates a reduced control voltage to thepower supply 27. Comparator 180 automatically monitors the reducedcontrol voltage, where −A2 is now less than +A2, to drive switch 160 on.The turn on of switch 160 redirects the stored energy of outputcapacitor 134. As a result, the redirected stored energy in the powersupply 27 lowers the output voltage Vc and rapidly reduces the deliveredRF energy of the RF output stage 28.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A generator for providing treatment energy totissue, comprising: a power supply having an output filter and adischarge circuit, the output filter configured to store and outputdirect current energy; an output stage coupled to the power supply andconfigured to convert the direct current energy into treatment energyfor use in treating tissue; and a controller configured to adjust atleast one of the power supply or the output stage to control the amountof treatment energy output by the output stage, wherein the dischargecircuit is configured to control a time rate change of a discharge ofthe direct current energy stored in the output filter away from theoutput stage based on a comparison between the direct current energystored in the output filter and a feedback signal generated byapplication of the treatment energy to tissue.
 2. A generator forproviding treatment energy to tissue according to claim 1, wherein thefeedback signal is based on at least one sensed tissue property.
 3. Agenerator for providing treatment energy to tissue according to claim 2,wherein the at least one sensed tissue property is derived based on anapplication of treatment energy output by the output stage to tissue. 4.A generator for providing treatment energy to tissue according to claim2, wherein the at least one sensed tissue property is an increase intissue impedance based on tissue desiccation.
 5. A generator forproviding treatment energy to tissue according to claim 1, furthercomprising a sensor operably coupled to the controller and configured tosense at least one tissue property.
 6. A generator for providingtreatment energy to tissue according to claim 5, wherein the feedbacksignal is generated by the sensor based on the at least one sensedtissue property.
 7. A generator for providing treatment energy to tissueaccording to claim 1, wherein the output filter is an LC circuit.
 8. Agenerator for providing treatment energy to tissue according to claim 1,wherein the treatment energy is RF energy.
 9. A generator for providingtreatment energy to tissue according to claim 1, wherein the controlleris configured to adjust at least one of the power supply or the outputstage to control the amount of treatment energy output by the outputstage in real time.
 10. A generator for providing treatment energy totissue, comprising: a power supply having an output filter and adischarge circuit, the output filter configured to store and outputdirect current energy; an output stage coupled to the power supply andconfigured to convert the direct current energy into treatment energyfor use in treating tissue; at least one sensor configured to sense atleast one tissue property based on the application of treatment energyto tissue and configured to generate a feedback signal based on the atleast one sensed tissue property; and a controller operably coupled tothe at least one sensor and configured to adjust at least one of thepower supply or the output stage to control the amount of treatmentenergy output by the output stage, wherein the discharge circuit isconfigured to provide time rate control of the discharge of the directcurrent energy stored in the output filter away from the output stagebased on a comparison between the direct current energy stored in theoutput filter and the feedback signal generated by the sensor.